Comparing the results of the application of moving and stationary sinusoidal gratings in the functionally assisted treatment of meridional amblyopia

Introduction: Background: The first approach to a frequency-selective visual training in amblyopia had been proposed in the sixties by the physiologist Fergus Campbell. During the stimulation, his grating was moving very slowly, i.e., only once a minute around its axis. Therefore, the CAM-stimulator was based exclusively on the proposed influence of spatial frequency selectivity, however there was no significant contribution of the temporal frequency of the stimulus. Accordingly, we are convinced that this was one of the main reasons for the failure of Campbell's approach after the evaluation by a multiple of placebo-controlled studies. The aim of the present work, therefore, was to investigate in the influence of visual exercises, which contained moving circular gratings as compared to such of stationary gratings implemented into computer games on the development of visual acuity. Especially we were interested in the effects of such type of visual exercises using a circular sinusoidal grating on the visual acuity development in patients with meridonal amblyopia. We assume, in particular, that such a ring-shaped stimulus can reach all angular positions equally, and thus excite the most ametropic meridians, as compared to the least ametropic meridians, in a particular way. Methods: Overall, we investigated in two groups of patients with meridional amblyopia who had been selected according to the age structure and to their type of disturbance. Using a cross-over design, the first group was alternately exercised 10 days with the moving followed by 10 days with the stationary grating stimulus, and the second group was alternately exercised 10 days with the stationary followed by 10 days with the moving grating stimulus, i.e. in reverse order. For the treatment, a sinusoidally modulated drifting grating had been implemented as a background stimulus into simple computer games. These games served for the attraction of attention of the children. For the present study these exercises were provided by the telemedical portal of the Amblyocation ltd. in the following two versions. The first version contained a concentric outward-moving ring-shaped sinusoidal grating behind of the computer games during the process of visual stimulation. The grating was fixed at a spatial frequency of 0.3 cyc/deg with the time frequency of 1 cyc/sec, which gave an angular velocity of 3.33 deg/sec. The second version of the program contained the same grating, but in a non-moving presentation. In order to additionally distinguish between the envisaged meridional stimulus effects, we examined our patients with regard to their corrected visual acuity using a directionally sensitive set of optical characters developed at the Kharkevich Institute. The monocular corrected visual acuity was tested in all patients at 4 meridians: 0, 45, 90 and 135 degrees. Additionally, in all patients of the first group and all patients of the second group, the binocular visual acuity was examined too. Results: In the measurements of the corrected visual acuity along four meridians, a statistically significant improvement was found with alignment of the directional optical characters close to the meridian with maximal ametropia, and the minimal improvement in the orientation perpendicular thereto. In the patients of the both groups, the corrected visual acuity had significantly increased as a result of the treatment performed in the stage with a series of exercises with the moving circular sinusoidal grating. After the stage of treatment using the stationary grating, however, there was found no statistically significant improvement. Conclusions: Telemedical exercises using special computer games that contained a moving circular sinusoidal grating resulted in a statistically significant positive dynamics of visual acuity development in the most ametropic meridian as compared to the least ametropic meridian. No statistically significant improvement was observed after exercises with the stationary grating.